> I think mainly for familiarity and out of loneliness

These aren't good reasons to get back together with anyone, please note what's glaringly missing: you didn't say anything to the effect of "she was the one that got away" or "I still love her". So do both of you a favor and don't come back into her life.

You also asked us to convince you that you shouldn't. So you already know that you shouldn't.